Viral infections can be associated with activation of eosinophils, especially in the airways of patients with asthma. We have demonstrated that eosinophils in the airways have a pronounced antiviral effect. Our studies suggest that this is due to metabolism of bromide by eosinophil peroxidase (EPO). Eosinophil ribonucleases (eosinophil derived neurotoxin (EDN) and eosinophil cationic protein (ECP)) may also participate. We propose to investigate the mechanisms of the antiviral effects of eosinophils. In specific aim #1, we will test the ability of human eosinophils to kill virus (parainfluenza, influenza, rhinovirus, and respiratory syncytial virus) in vitro. The requirement for bromide will be tested, as will the role of eosinophil ribonucleases. We will determine whether direct contact of the eosinophil with the virus is required and, if so, whether interactions of virus attachment proteins with specific cellular receptors is involved. We will also isolate the eosinophils from wild type and EPO (-/-) mice, and test their antiviral properties in vitro. In specific aim #2, we will test the ability of purified human EPO, EDN, and ECP, as well as eosinophil major basic protein, to kill viruses in vitro. The bromide dependence of this reaction will be determined, and the potency of the antiviral properties of the various eosinophil proteins for the four viruses listed above will be determined. In specific aim #3, we will test the ability of eosinophils to kill virus in vivo in wild type, in EPO (-/-), in IL-5 transgenic mice, and in mice that are EPO (-/-) on an IL-5 transgenic background. The effects of reversing eosinophilia using monoclonal antibodies to IL-5 and to VLA4 will be determined. In specific aim #4, we will use an ex vivo preparation in which the lungs of antigen challenged mice will be infected with viruses in vitro under various bromide concentrations and in the presence or absence of ribonuclease inhibitors. These studies will advance our understanding of the beneficial role of eosinophils in the airways, and may suggest new therapeutic strategies for both viral infections and allergic airway disease. [unreadable] [unreadable]